Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ import java.io.IOException; import java.io.InputStream; import java.io.Reader; /** * Reader for UCS-2 and UCS-4 encodings. (i.e., encodings from * ISO-10646-UCS-(2|4)). * * @xerces.internal * * @author Neil Graham, IBM * * @version $Id: UCSReader.java 449317 2006-09-23 22:12:30Z mrglavas $ */ public class UCSReader extends Reader { // // Constants // /** * Default byte buffer size (8192, larger than that of ASCIIReader since it's * reasonable to surmise that the average UCS-4-encoded file should be 4 times * as large as the average ASCII-encoded file). */ public static final int DEFAULT_BUFFER_SIZE = 8192; public static final short UCS2LE = 1; public static final short UCS2BE = 2; public static final short UCS4LE = 4; public static final short UCS4BE = 8; // // Data // /** Input stream. */ protected final InputStream fInputStream; /** Byte buffer. */ protected final byte[] fBuffer; // what kind of data we're dealing with protected final short fEncoding; // // Constructors // /** * Constructs a UCS reader from the specified input stream using the default * buffer size. The Endian-ness and whether this is UCS-2 or UCS-4 needs also * to be known in advance. * * @param inputStream * The input stream. * @param encoding * One of UCS2LE, UCS2BE, UCS4LE or UCS4BE. */ public UCSReader(InputStream inputStream, short encoding) { this(inputStream, DEFAULT_BUFFER_SIZE, encoding); } // <init>(InputStream, short) /** * Constructs a UCS reader from the specified input stream and buffer size. * The Endian-ness and whether this is UCS-2 or UCS-4 needs also to be known * in advance. * * @param inputStream * The input stream. * @param size * The initial buffer size. * @param encoding * One of UCS2LE, UCS2BE, UCS4LE or UCS4BE. */ public UCSReader(InputStream inputStream, int size, short encoding) { this(inputStream, new byte[size], encoding); } // <init>(InputStream,int,short) /** * Constructs a UCS reader from the specified input stream and buffer. The * Endian-ness and whether this is UCS-2 or UCS-4 needs also to be known in * advance. * * @param inputStream * The input stream. * @param buffer * The byte buffer. * @param encoding * One of UCS2LE, UCS2BE, UCS4LE or UCS4BE. */ public UCSReader(InputStream inputStream, byte[] buffer, short encoding) { fInputStream = inputStream; fBuffer = buffer; fEncoding = encoding; } // <init>(InputStream,int,short) // // Reader methods // /** * Read a single character. This method will block until a character is * available, an I/O error occurs, or the end of the stream is reached. * * <p> * Subclasses that intend to support efficient single-character input should * override this method. * * @return The character read, as an integer in the range 0 to 127 (<tt>0x00-0x7f</tt>), * or -1 if the end of the stream has been reached * * @exception IOException * If an I/O error occurs */ public int read() throws IOException { int b0 = fInputStream.read() & 0xff; if (b0 == 0xff) { return -1; } int b1 = fInputStream.read() & 0xff; if (b1 == 0xff) { return -1; } // UCS-4 if (fEncoding >= 4) { int b2 = fInputStream.read() & 0xff; if (b2 == 0xff) { return -1; } int b3 = fInputStream.read() & 0xff; if (b3 == 0xff) { return -1; } if (fEncoding == UCS4BE) { return (b0 << 24) + (b1 << 16) + (b2 << 8) + b3; } return (b3 << 24) + (b2 << 16) + (b1 << 8) + b0; } // UCS-2 if (fEncoding == UCS2BE) { return (b0 << 8) + b1; } return (b1 << 8) + b0; } // read():int /** * Read characters into a portion of an array. This method will block until * some input is available, an I/O error occurs, or the end of the stream is * reached. * * @param ch * Destination buffer * @param offset * Offset at which to start storing characters * @param length * Maximum number of characters to read * * @return The number of characters read, or -1 if the end of the stream has * been reached * * @exception IOException * If an I/O error occurs */ public int read(char ch[], int offset, int length) throws IOException { int byteLength = length << ((fEncoding >= 4) ? 2 : 1); if (byteLength > fBuffer.length) { byteLength = fBuffer.length; } int count = fInputStream.read(fBuffer, 0, byteLength); if (count == -1) return -1; // try and make count be a multiple of the number of bytes we're looking for if (fEncoding >= 4) { // BigEndian // this looks ugly, but it avoids an if at any rate... int numToRead = (4 - (count & 3) & 3); for (int i = 0; i < numToRead; i++) { int charRead = fInputStream.read(); if (charRead == -1) { // end of input; something likely went wrong!A Pad // buffer with nulls. for (int j = i; j < numToRead; j++) { fBuffer[count + j] = 0; } break; } fBuffer[count + i] = (byte) charRead; } count += numToRead; } else { int numToRead = count & 1; if (numToRead != 0) { count++; int charRead = fInputStream.read(); if (charRead == -1) { // end of input; something likely went wrong!A Pad // buffer with nulls. fBuffer[count] = 0; } else { fBuffer[count] = (byte) charRead; } } } // now count is a multiple of the right number of bytes int numChars = count >> ((fEncoding >= 4) ? 2 : 1); int curPos = 0; for (int i = 0; i < numChars; i++) { int b0 = fBuffer[curPos++] & 0xff; int b1 = fBuffer[curPos++] & 0xff; // UCS-4 if (fEncoding >= 4) { int b2 = fBuffer[curPos++] & 0xff; int b3 = fBuffer[curPos++] & 0xff; if (fEncoding == UCS4BE) { ch[offset + i] = (char) ((b0 << 24) + (b1 << 16) + (b2 << 8) + b3); } else { ch[offset + i] = (char) ((b3 << 24) + (b2 << 16) + (b1 << 8) + b0); } } else { // UCS-2 if (fEncoding == UCS2BE) { ch[offset + i] = (char) ((b0 << 8) + b1); } else { ch[offset + i] = (char) ((b1 << 8) + b0); } } } return numChars; } // read(char[],int,int) /** * Skip characters. This method will block until some characters are * available, an I/O error occurs, or the end of the stream is reached. * * @param n * The number of characters to skip * * @return The number of characters actually skipped * * @exception IOException * If an I/O error occurs */ public long skip(long n) throws IOException { // charWidth will represent the number of bits to move // n leftward to get num of bytes to skip, and then move the result // rightward // to get num of chars effectively skipped. // The trick with &'ing, as with elsewhere in this dcode, is // intended to avoid an expensive use of / that might not be optimized // away. int charWidth = (fEncoding >= 4) ? 2 : 1; long bytesSkipped = fInputStream.skip(n << charWidth); if ((bytesSkipped & (charWidth | 1)) == 0) return bytesSkipped >> charWidth; return (bytesSkipped >> charWidth) + 1; } // skip(long):long /** * Tell whether this stream is ready to be read. * * @return True if the next read() is guaranteed not to block for input, false * otherwise. Note that returning false does not guarantee that the * next read will block. * * @exception IOException * If an I/O error occurs */ public boolean ready() throws IOException { return false; } // ready() /** * Tell whether this stream supports the mark() operation. */ public boolean markSupported() { return fInputStream.markSupported(); } // markSupported() /** * Mark the present position in the stream. Subsequent calls to reset() will * attempt to reposition the stream to this point. Not all character-input * streams support the mark() operation. * * @param readAheadLimit * Limit on the number of characters that may be read while still * preserving the mark. After reading this many characters, * attempting to reset the stream may fail. * * @exception IOException * If the stream does not support mark(), or if some other I/O * error occurs */ public void mark(int readAheadLimit) throws IOException { fInputStream.mark(readAheadLimit); } // mark(int) /** * Reset the stream. If the stream has been marked, then attempt to reposition * it at the mark. If the stream has not been marked, then attempt to reset it * in some way appropriate to the particular stream, for example by * repositioning it to its starting point. Not all character-input streams * support the reset() operation, and some support reset() without supporting * mark(). * * @exception IOException * If the stream has not been marked, or if the mark has been * invalidated, or if the stream does not support reset(), or if * some other I/O error occurs */ public void reset() throws IOException { fInputStream.reset(); } // reset() /** * Close the stream. Once a stream has been closed, further read(), ready(), * mark(), or reset() invocations will throw an IOException. Closing a * previously-closed stream, however, has no effect. * * @exception IOException * If an I/O error occurs */ public void close() throws IOException { fInputStream.close(); } // close() } // class UCSReader